The present invention relates to camera focusing devices.
It has already been proposed to provide for detection of proper focus of a camera from the knowledge that various factors such as contrast, spatial frequency, and luminance of an object to be photographed vary in accordance with the accuracy of focusing. Thus, it is known according to one prior art procedure to utilize for this purpose photosensitive elements such as cadmium sulfide elements having specific contrast-responsive characteristics. However, this latter procedure has a considerable disadvantage in that it is difficult to prepare the elements with uniform photoresponsive characteristics, and in addition the output variation of such photosensitive elements before and after the properly focused position is too low to achieve an exact detection insofar as detection of proper focusing at low luminance is concerned.
A second type of known focusing expedient utilizes a photoelectric output signal obtained by oscillating or rotating an optical member in a mechanical manner. This type of procedure also has a considerable disadvantage in that mechanically movable parts are required and thus miniaturization of a camera is prevented while at the same time the required power consumption is increased. A third type of expedient utilizes two outputs from two sets of photodetective members arranged at different positions in the same way as in a so-called coupled range-finding camera. This third expedient also has a disadvantage in that with such an arrangement it is extremely difficult to provide for interchangeable lenses.